How to clean a heat transfer oil furnace?

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This post was last edited by sunjl1981 on March 5, 2016, at 10:11. To clean a thermal oil furnace, one must first analyze and determine the specific usage conditions of the furnace in their own factory. It is necessary to decide which thermal oil cleaning agent to use and ultimately determine the cleaning procedure. As an excellent heat transfer medium, heat transfer oil (organic heat carrier) features heat transfer under high temperature and low pressure conditions. It offers high thermal efficiency, uniform heat distribution, accurate temperature control, as well as significant energy-saving benefits. However, whether it is synthetic or mineral-based, heat transfer oil is an organic substance – namely alkanes, cycloalkanes, aromatics, and their derivatives. They will undergo pyrolysis when operating for long periods in hot oil furnaces at high temperatures. The coking and carbonization that occur during the use of heat transfer oil create an insulating layer, which leads to a reduced heat transfer efficiency, an increase in flue gas temperature, and higher fuel consumption ； On the other hand, due to the temperature requirements of the production process, the temperature difference across the wall of the heating furnace tube increases sharply. If this temperature difference between the inside and outside of the furnace tube reaches 600–700°C, it is very likely that the tube will be burned through, leading to fire safety accidents. Heat transfer oil furnace cleaners mainly rely on a combination of three basic components: alkalis, organic solvents, and surfactants (referred to as SAA). Other additives such as chelating agents, oxidizers, corrosion inhibitors, adsorbents, and anti-deposition agents are also included. Through processes like heating and mechanical scrubbing, these cleaners achieve the goal of removing carbon deposits from the system. The coking-cleaning effect of cleaning agents is achieved through the solubilization, wetting, adsorption, emulsification, and dispersion of surfactants. ①Two-step process of alkaline cleaning and acid cleaning: drain the heat transfer oil → purge residual oil with steam → use an alkaline cleaner → rinse with water → acid clean → passivate → completion. Principle: Alkaline water-based cleaners are effective in removing medium-temperature carbon deposits in oils, but a dense layer of graphitized high-temperature carbon deposits remains on the inner surface of the test pieces after treatment. Therefore, further acid washing is required to remove these residual carbon layers, so as to prevent them from affecting the quality of the heat transfer oil and its heat transfer efficiency. The two-step cleaning process of alkali washing and acid washing is used to remove carbon deposits from heat transfer boilers and pipelines, offering advantages such as high cleaning efficiency, low cleaning temperatures, non-toxicity, and low cleaning costs. Although this method can remove scale deposits, it involves numerous procedures; it causes acid and alkali corrosion, shortens the lifespan of the machinery, leads to secondary pollution, and must be carried out while the heat transfer oil furnace is shut down, which affects production. ②Dissolution cleaning process: Drain the heat transfer oil → Purge residual oil with steam → Clean with an organic solvent solution (organic solvent + SAA + additives) → Passivate. Principle: Since coke scale is a complex mixed scale primarily composed of organic substances, its adhesion to metal surfaces is due to physical adsorption via van der Waals forces. The \"dissolution washing method\" is used, in which tar is dissolved in an organic solvent, and as the organic substances dissolve, the scale is removed naturally. This cleaning agent has a quite strong cleaning power and is not greatly affected by temperature. After cleaning with this detergent, it is treated through clarification and filtration; by adding an appropriate amount of surfactants and additives, it can be reused. The residue can be mixed into coal for combustion, reducing costs and environmental pollution. However, this cleaning agent is volatile, has low safety, and high costs. ③Process of composite cleaning agent cleaning method: Drain the heat transfer oil → Purge residual oil with steam → Clean using a circulating cleaning solution. Principle: The composite cleaning agent mainly consists of several surfactants; with the assistance of auxiliary cleaning agents, these surfactants first adsorb onto the surface of oil stains, wetting and expanding them. Thereafter, the cleaning agent penetrates into the gaps between the oil stains, causing the oil contaminants to gradually form micelles as a result of the action of the composite cleaning agent. Through continuous circulation driven by a pump, the dispersed and emulsified oil contaminants can be removed from the heat transfer surface. This cleaning agent can effectively break down and disperse carbon deposits, as well as efficiently dissolve organic hydrocarbons; it has a simple process and causes little to no corrosion to equipment. However, this method causes secondary pollution and requires cleaning while the machine is stopped, which affects production. ④Organic additive cleaning process: Simply adding an additive to the operating heat transfer oil allows the carbon deposits to flake off, after which the oil residues are removed through clarification and filtration. Principle: This additive utilizes the principle of like dissolves like to elute tar deposits or degrade them, thereby preventing the deterioration of heat transfer oil. This method enables cleaning without stopping the process; the additive can withstand high temperatures of over 260°C, dissolve in heat transfer oil without affecting its properties, and its usage amount can exceed 5% of that of the heat transfer oil. When in use, the heat transfer oil furnace and pipelines do not need to be cooled, which does not affect production. This method is simple and cost-effective; the heat transfer oil after the removal of oil residues can be reused without polluting the environment, representing a trend in using chemical cleaning methods for cleaning heat transfer oil pipelines.